<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/09/01/customizing-a-flex-tooltip-instances-appearance-using-styles/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:Style>
        ToolTip {
            backgroundColor: black;
            backgroundAlpha: 1.0;
            cornerRadius: 0;
            color: white;
        }
    </mx:Style>

    <mx:Button label="Roll over to see tool tip"
            toolTip="The quick brown fox jumped over the lazy dog." />

</mx:Application>